We want to ensure that targeting invalid minions does *not* allow us to
run any sort of shenanigans on the minions in question! This ensures
that valid commands (i.e. file.touch in this case) cannot inadvertently
be sent to minions that we don't have ACL for.

It's possible that the output of ls is different for some reason, but
test -f should always return 0 if the file exists, or 1 otherwise. We
want it to be not 0.